Liu, A. G. S. C., Menon, L., Shields, G., Callow, R., & McIlroy, D. (2017).Martin Brasier’s contribution to the palaeobiology of theEdiacaran–Cambrian transition. Geological Society Special Publications,448(1), 179-183. https://doi.org/10.1144/SP448.9

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Martin Brasier’s contribution to the palaeobiology of the Ediacaran–Cambrian 1

transition 2

ALEXANDER G. LIU1, LATHA R. MENON2, GRAHAM A. SHIELDS3, RICHARD H. T. CALLOW4 & 3

DUNCAN MCILROY5 4

5 1 School of Earth Sciences, University of Bristol, 24 Tyndall Avenue, Bristol, BS8 1TQ, U.K. 6 2 Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, 7

Oxfordshire, OX1 3AN, U.K. 8 3 Department of Earth Sciences, University College London, Gower Street, London WC1E 9

6BT, U.K. 10 4 Statoil ASA, 4035 Stavanger, Norway. 11 5 Department of Earth Sciences, Memorial University of Newfoundland, 300 Prince Philip 12

Drive, St. John’s, NL, A1B 3X5, Canada. 13

14

Abstract 15

Martin Brasier’s work spanned almost the entire geological column, but the origin of animals 16

and the nature of the Cambrian Explosion were areas of particular interest. Martin adopted a 17

holistic approach to the study of these topics that considered the interplay between multiple 18

geological and biological phenomena, and sought to interpret the fossil record within the 19

broad context of geological, biogeochemical, and ecological changes in the Earth system. 20

Here we summarize Martin’s main contributions in this area, and assess the impact of his 21

findings on the development of this field. 22

23

“Karl Popper would have said that… palaeontology [is] not real science because 24

you can’t go out and sample it. I think absolutely the opposite. I think this is 25

actually where science is. It’s trying to guess what lies over the hill and map terra 26

incognita. When people come in and colonize, that’s just technology.” 27

Martin Brasier, 2013 28

(Excerpted from a phone interview with Robert Moor, On Trails, 2016) 29

30

Martin’s path into the Ediacaran–Cambrian transition 31

Martin Brasier frequently articulated the story of his journey into the study of the Cambrian 32

Explosion of animal life. Drawing comparisons to Darwin and Lyell, Martin observed that his 33

research into the past also began by looking at the present – in his case, exploring Caribbean 34

reefs and lagoons as a ship’s naturalist on-board HMS Fawn and HMS Fox during his 35

doctoral work in 1970 (Brasier 2009). Much of his early palaeontological research focused on 36

Foraminifera (see Brasier 2012; Gooday in review), but these interests broadened to 37

encompass other groups and ever more ancient organisms. During his time at the University 38

of Reading, Martin was shown macrofossil specimens from the Ediacaran of Australia by 39

Roland Goldring, which Martin later quipped he didn’t study at the time because “[the 40

Ediacara biota] had been solved, Glaessner had worked it all out”. Martin did however take 41

an interest in Roland’s archaeocyathid sponges, which led him to Paris to work with 42

Françoise Debrenne on the Cambrian Explosion. 43

Martin became fascinated by the conundrum of Darwin’s Dilemma: the mystery of 44

why animal fossils seemingly extended back in time only to the Cambrian Period when 45

evolutionary theory predicted a much more ancient history for metazoan lineages. He saw the 46

Cambrian Explosion as “probably one of the strangest things that’s ever happened to life on 47

our planet”, and dedicated a significant amount of his career to attempting to resolve this 48

problem. An early contribution to this area involved helping Michael House to organize one 49

of the first symposia on the Cambrian Explosion, for the Systematics Association in 1978. 50

Meanwhile, work at the University of Hull explored the ecology and taphonomy of 51

archaeocyaths and the “Tommotian” trace fossils and skeletal biota of Nuneaton: the Small 52

Shelly Fossils, or “small smelly fossils” as Martin fondly referred to them (Brasier 1976, 53

1984, 1986; Brasier et al. 1978; Brasier & Hewitt 1979). Those studies later expanded to 54

encompass the broader Cambrian Explosion, and particularly its global palaeoenvironmental 55

context (Brasier 1982, 1985). 56

Following his move to the University of Oxford in 1988, Martin became focused on 57

the interrelationship between the evolution of animal life, nutrient flux, and the global ocean-58

atmosphere system, as evidenced by authigenic minerals and geochemistry (e.g. Brasier 59

1990, 1991, 1992; Brasier et al. 1990; Brasier et al. 1992). His arrival in Oxford coincided 60

with a surge in interest in carbon isotope perturbations around the Ediacaran–Cambrian 61

boundary (Hsu et al. 1985; Knoll et al. 1986; Magaritz et al. 1986; Tucker 1986). With a 62

stable isotope laboratory at his disposal, Martin became an isotope enthusiast, launching a 63

series of chemostratigraphic studies through the 1990’s, spurred on by a healthy rivalry with 64

the competing Harvard group (e.g. Knoll et al. 1995). His interest in isotopes refined stable 65

isotope stratigraphy across the Ediacaran–Cambrian boundary, culminating, through his 66

involvement in the International Subcommission on Cambrian Stratigraphy, with an 67

internationally agreed definition for the basal Cambrian boundary (Brasier et al. 1994a; 68

Landing & Geyer this volume). By the end of the decade, Martin had fully incorporated 69

global isotopic trends into a holistic synthesis of the Ediacaran–Cambrian transition (Brasier 70

& Lindsay 2001) that had its roots 20 years earlier (Brasier 1980, 1982). 71

Between 1992 and 1995, Martin supervised his first student on the Ediacaran–72

Cambrian transition, Duncan McIlroy, and it was at this time that Martin was partly drawn 73

away from the carbonate-rich Cambrian successions and towards the fossiliferous siliciclastic 74

Ediacaran–Cambrian sections of Avalonia and Baltica (Brasier & McIlroy 1998; McIlroy et 75

al. 1998). It was not until the early 2000s that Martin truly engaged with the Ediacaran during 76

a visit to Mistaken Point with Guy Narbonne of Queens University. Following McIlroy’s 77

move to Memorial University of Newfoundland (Canada), Martin became an adjunct 78

professor at Memorial University, and from 2005 onwards he visited Newfoundland with 79

graduate students for several weeks each year (Fig. 1) until his death. Many of these students, 80

including Jonathan Antcliffe, Richard Callow, Alex Liu, Latha Menon, Jack Matthews and 81

Renee Hoekzema, continue to explore aspects of Ediacaran geology and palaeobiology in 82

Newfoundland and elsewhere. Although Martin extended his research ever further back in 83

time, “working on ever older and more puzzling rocks – as I myself grew more ancient and 84

puzzled” (see Antcliffe et al. this volume), the question of animal origins, and the enigma of 85

the Cambrian Explosion, remained a core area of his studies. Some of the highlights of his 86

Ediacaran and Cambrian work, and their intellectual impact on the field, are outlined below. 87

88

Refining stratigraphic understanding 89

Martin’s work, particularly in the 1980s and 1990s, had a strong focus on refining Ediacaran–90

Cambrian stratigraphy in order to develop a global framework upon which to pin geological 91

and evolutionary events. He noted at his retirement event in 2014 that “although everybody 92

is interested in the biology of the Cambrian Explosion, actually defining the terms and the 93

nature of rocks across that time was a fundamental part of developing the language we 94

needed…”. As part of his formal Reply upon receiving the Lyell Medal of the Geological 95

Society that same year, he noted: “It took twenty years (1973–1993) to help settle a definition 96

of the Precambrian–Cambrian boundary, and another two decades to help characterize the 97

new Ediacaran System”. 98

Martin’s involvement in this important work utilized several independent records, 99

across multiple continents. Following early work on the Cambrian boundary sections in India 100

(Brasier & Singh 1987), he proceeded to integrate geochemical and biostratigraphic records 101

from places as far afield as Scotland, Iran, Oman, China, Mongolia, Spain and Australia, 102

demonstrating thereby major discontinuities in classic GSSP candidate sections (Brasier et al. 103

1979; Brasier, et al. 1990; Brasier et al. 1996; Shields et al. 1997; Brasier & Shields 2000; 104

Lindsay et al. 2005). These studies contributed to an increasingly robust understanding of 105

temporal changes in geochemical records during the Ediacaran–Cambrian transition, and also 106

include some of the first publications to recognise overlaps in the biostratigraphic ranges of 107

key Cambrian biotas (e.g. Brasier et al. 1979). Although he was not a geochronologist, 108

Martin became associated with several projects involved in dating significant Ediacaran and 109

Cambrian sections worldwide, including studies of material from Oman (Brasier et al. 2000), 110

and most recently efforts to date the fossiliferous Ediacaran localities in Newfoundland. 111

Martin became involved in global discussions regarding Cambrian stratigraphic 112

correlation during the late 1980s and early 1990s, holding positions as Secretary of the 113

Working Group on the Precambrian–Cambrian boundary, and leader of IGCP Project 303 on 114

Precambrian–Cambrian event stratigraphy (Brasier et al. 1994b). Most notably, in his role as 115

President of the International Subcommission on Cambrian Stratigraphy (1992–1996) Martin 116

presided over the key decision regarding the placement of the Global Stratotype Section and 117

Point for the base of the Cambrian System. This process required considerable diplomacy, 118

with multiple nations competing for the GSSP (Brasier et al. 1994a; Brasier 2009). The 119

eventual GSSP section, at Fortune Head in Newfoundland, was chosen partly on the basis of 120

its possession of the first appearance datum of the Treptichnus pedum (formerly Phycodes 121

pedum) trace fossil assemblage (summarized in Brasier et al. 1994a; McIlroy & Brasier this 122

volume). Although this decision has largely withstood the test of time, refinement of formal 123

stratigraphy in both the Cambrian and the Neoproterozoic are ongoing (e.g. Narbonne et al. 124

2012; Shields-Zhou et al. 2012; Landing et al. 2013; Babcock et al. 2014; Geyer & Landing 125

this volume). Martin retained an active role in Subcommission activities, and was a Voting 126

Member of the International Subcommission on Ediacaran Stratigraphy at the time of his 127

death. 128

129

Decoding the Ediacaran biota 130

Martin worked on several different groups of Cambrian and Neoproterozoic organisms, but 131

perhaps the most challenging (and ultimately rewarding) group were the Ediacaran soft-132

bodied macrobiota. To the uninitiated, study of the Ediacaran macrobiota appears a daunting 133

task: many of the fossils bear little or no resemblance to any extinct or extant taxon, and their 134

paucity of recognisable morphological characters has contributed to significant uncertainty 135

regarding their position in the eukaryotic tree. Martin conducted fieldwork in locations 136

including Canada, Oman, Namibia and Brazil to attempt to resolve the question of what the 137

Ediacaran organisms were. The consensus opinion when Martin began his Ediacaran–138

Cambrian research was that many of the Ediacaran macro-organisms were animals (cf. 139

Glaessner 1984), but following Seilacher’s famous suggestion of an alternative Vendobiont 140

hypothesis (Seilacher 1984, 1989), considerable debate and uncertainty has surrounded their 141

phylogenetic position. Martin was keen to emphasize that the Precambrian world was 142

different, and that the principle of uniformitarianism could not be extrapolated back into the 143

Precambrian as reliably as it could in the Phanerozoic: “the world before the Cambrian was, 144

arguably, more like a distant planet” (Brasier 2009). He also recognized that ‘shoehorning’ 145

Ediacaran fossils into modern groups was unwise, since many characters diagnostic of extant 146

crown groups were likely to have developed in response to extrinsic events or factors that had 147

not yet come to pass in the Ediacaran. In particular, he was in recent years a vocal advocate 148

of questioning the assumption that many Ediacaran macro-organisms were metazoan, 149

critically assessing the evidence, promoting consideration of the null hypothesis, and 150

encouraging debate and discussion (e.g. Antcliffe et al. 2014). Where the evidence weighed 151

against the null hypothesis, however, he remained open to the possibility that some Ediacaran 152

forms might represent simple animals (e.g. Liu et al. 2015b). 153

Although he participated in field trips to Ediacaran localities from the 1970s onwards, 154

it was only in the early 2000s that Martin started to seriously examine Ediacaran 155

macrofossils, with his first foray in this field being a Masters student project on Charnia 156

masoni (completed by Jo Slack). This led to over a decade of research into the Ediacaran 157

macrobiota, which coincided with a significant global invigoration of the field. Perhaps 158

unsurprisingly, this work also included occasional descriptions of microfossils (e.g. Zhou et 159

al. 2001). 160

161

Consideration of growth and development 162

Martin’s approach to investigating Ediacaran macro-organisms was to focus on a small 163

number of iconic, representative taxa; to study these in detail; and to assess their growth and 164

development in order to attempt to constrain their phylogenetic position (an approach 165

outlined in Brasier & Antcliffe 2004). Work undertaken with Jonathan Antcliffe on Charnia 166

demonstrated how its mode of growth seemingly differs from that of extant sea pens, thus 167

permitting a pennatulacean affinity for Charnia to be refuted (Antcliffe & Brasier 2007a, 168

2008). Similar studies into Dickinsonia (Brasier & Antcliffe 2008; utilising specimens from 169

the Goldring collection) and Palaeopascichnus (Antcliffe et al. 2011) provided further 170

contributions to our knowledge of those taxa and their construction, and expanded the 171

armoury of approaches used to examine Ediacaran macrofossils. The influence of this work 172

can be clearly seen in recent studies into the growth, development and morphogenesis of 173

Ediacaran macrofossils (e.g. Hoyal Cuthill & Conway Morris, 2014; Gold et al. 2015). 174

Martin’s studies also introduced a technological innovation to Ediacaran palaeobiology: the 175

laser scanning of fossil-bearing surfaces (Fig. 2; Antcliffe & Brasier 2011). Laser scanning 176

permits fine-scale quantitative studies of morphology, and reveals morphological characters 177

that cannot be easily observed in the field. 178

Consideration of other Ediacaran frondose taxa (e.g. Bradgatia and Charniodiscus) 179

explored how those organisms might be related to one another (Brasier & Antcliffe 2004, 180

2009), how disparate their morphologies could be (Antcliffe & Brasier 2007b) and the details 181

of their architecture and taxonomy, culminating in the development of a coherent system with 182

which to describe and classify rangeomorph organisms (Brasier et al. 2012). That latter 183

publication provided a testable framework in which to explore frondose taxa, and has 184

stimulated ongoing research into the fundamental question of what constitutes ecophenotypic 185

versus genotypic variability in Ediacaran populations (e.g. Wilby et al. 2015; Liu et al. 2016). 186

Though he did not describe significant numbers of new Ediacaran macrofossil taxa, Martin 187

was particularly proud of deciphering Beothukis mistakensis (Brasier & Antcliffe 2009), 188

which he considered to be a ‘Rosetta Stone’ for the understanding of rangeomorphs. As with 189

the other taxa he named from Newfoundland (e.g. Vinlandia, Brasier et al. 2012), Martin 190

favoured names that celebrated the history of the island and the language of its indigenous 191

populations. 192

193

A focus on Avalonia 194

Martin’s work included descriptions of Ediacaran fossils from Australia (Brasier & Antcliffe 195

2008), Iran (Menon et al. In Prep), Brazil (Parry et al. In Prep) and Siberia (Liu et al. 2013), 196

but much of his Ediacaran research was undertaken on sites either in England, or in 197

Newfoundland. The classic English localities of the Long Mynd and Charnwood Forest, 198

along with the coastal sections of Newfoundland, all lay on the margins of the microcontinent 199

of Avalonia during late Ediacaran times (Cocks et al. 1997). As such, they exhibit many 200

similarities in age, facies and fossil assemblage (Wilby et al. 2011; Noble et al. 2015), and in 201

the past decade Martin made a concerted effort to better understand these regions and their 202

relationship to wider global patterns and processes. 203

204

Charnwood Forest 205

The Ediacaran–Cambrian inlier of Charnwood Forest in Leicestershire, central England, was 206

for Martin a classic place to take new students due to its accessibility, its historical 207

importance in Ediacaran palaeontology, and because it is not a very easy area to understand 208

without geological mapping and careful fieldwork. The art of deciphering stratigraphy and 209

palaeoenvironment is something that Martin always loved, be it mapping the location of 210

Precambrian cherts (e.g. Wacey et al. 2010) or working out field relations between dated 211

igneous rocks and Ediacaran successions to indirectly constrain the age of the Ediacaran biota 212

(McIlroy et al. 1998). 213

The Charnian successions became a central focus of Martin’s research following his 214

2005 visit to Mistaken Point in Newfoundland, during which time his Oxford group first 215

started to develop ideas pertaining to growth and morphology of the Ediacaran macro-216

organisms. The easy accessibility of type material of Charnia masoni and Bradgatia 217

linfordensis allowed Martin to employ his skills as an artist to create sketches that were more 218

informative than any individual photograph. Martin used a technique where he drew the 219

same fossil multiple times using illumination from different directions to build up a picture of 220

the specimen that was simultaneously lit from several directions (Fig. 3). Although he called 221

it ‘camera lucida’, in truth it often involved him tracing over images directly on his computer 222

monitor. While drawing the type material of Charniodiscus, Martin suggested that it might 223

actually be composed of several fronds orientated at angles to one another and compressed 224

into the same plane (unpublished work discussed widely at conferences; Fig. 3; contrast this 225

with Brasier & Antcliffe 2009, fig. 12), which, if correct, potentially has implications for all 226

the other currently valid species of Charniodiscus (C. arboreus, C. longus, C. oppositus, C. 227

procerus, C. spinosus and C. yorgensis), which appear to only have one frond and as such 228

would have to be transferred to another genus. Charniodiscus is a particularly problematic 229

taxon, and although progress is being made in understanding its morphology (e.g. Ivantsov 230

2016), it remains to be seen whether Martin’s interpretation is correct. Much of Martin’s 231

work on rangeomorphs utilized material from Charnwood, and he also contributed to 232

discussions regarding protection of the Charnwood localities in his role as a member of the 233

Charnia Research Group. 234

235

The Long Mynd, Shropshire 236

The other main English Ediacaran sections are to be found on the Long Mynd of Shropshire. 237

The purported macrofossils from this area were first described by John Salter (Salter 1856, 238

1857) who was a contemporary of Charles Darwin, and the material from the Long Mynd 239

was posited by Darwin as a partial solution to the unexpectedly sudden appearance of fossils 240

at the base of what we now call the Cambrian Explosion (Darwin 1859). Martin had been 241

fond of relating the sad story of John Salter, who was from a relatively humble background 242

and had worked his way up to be a palaeontologist for the British Geological Survey, only to 243

be sacked just before reaching pensionable age. Struggling to support his family, and 244

suffering from bouts of depression, he finally committed suicide (Callow et al. 2011). In the 245

course of Martin’s revisiting of the Longmyndian fossils, the wonderful Darwin 246

Correspondence Project (e.g. Burkhardt & Smith 1985) provided a more complete story of 247

Salter’s last years, which lends support to the idea that he suffered from what we would now 248

call bipolar disorder (Callow et al. 2011). Salter’s tragic story, especially the way that his 249

work was overlooked and side-lined, touched Martin, who took delight in bringing Salter’s 250

work to a modern audience within the context of historical geology. 251

The key scientific questions regarding the Longmyndian relate to what its dominantly 252

discoidal fossil assemblage represents, and how the shallow-marine to fluvial depositional 253

environments relate to the largely marine sections seen elsewhere in Avalonia. The various 254

discoidal structures of the Long Mynd have been the subject of much discussion in the 255

geological literature (summarised in Callow & Brasier 2009a; Callow et al. 2011). Debate 256

had surrounded the biogenicity of the small, circular impressions from the Burway, Synalds 257

and Lightspout formations, with interpretations ranging from gas escape structures or 258

raindrops to body and trace fossils of Ediacaran macro-organisms (e.g. Cobbold 1900; 259

McIlroy et al. 2005; Toghill 2006). Martin’s own investigations in the Long Mynd led to 260

expanded descriptions of microfossils (originally described by Timofeyev et al. 1980, and 261

Peat 1984), and the recognition that they could be preserved in multiple taphonomic styles 262

(Callow & Brasier 2009b). Follow-up work with Latha Menon investigated the problem of 263

what the discoidal structures actually represent by utilising serial grinding techniques to 264

digitally reconstruct their three-dimensional morphology. This work revealed that the 265

Longmyndian discoidal impressions were formed by the interaction of escaping fluids within 266

finely laminated, microbial-mat-bound sediments (Menon et al. 2016; Menon et al. this 267

volume), finally establishing that they arose from a combination of abiogenic processes and 268

the presence of microbial mats. 269

So from a position where Martin felt that the Longmyndian sections were key to 270

understanding evolution in the latest Ediacaran (his Kotlin Crisis; Brasier 1995), gradually, 271

taxon by taxon, detailed objective work has reduced us to a position where there are no 272

longer any authentic Ediacaran macrofossils reported from the Long Mynd (though that is not 273

to say his Kotlin Crisis has been abandoned; see for example Kolesnikov et al. 2015). John 274

Salter’s novel assertion that there was Precambrian animal life is correct (Salter 1856), but 275

sadly not based on the material he knew. The critical reassessment of the discoidal forms of 276

the Long Mynd owe much to Martin instilling into his students the importance of constant 277

vigilance in interpreting ancient markings, and his emphasis on the importance of the null 278

hypothesis. In this case, the influence of microbial mats on fluid-filled sediments, driving 279

millimetre-scale fluid escape, and affecting their surface expression, was entirely sufficient to 280

explain the range of discoidal markings found on the Long Mynd. This work also expanded 281

the range of influence of microbial mats on Ediacaran sediments, and highlighted the need to 282

recognize the key role of microbes when examining the fossil record - a subject close to 283

Martin’s heart (e.g. Callow & Brasier 2009a; Brasier et al. 2010). 284

Meanwhile Martin’s interests in determining the origin of the Long Mynd’s other 285

enigmatic surface impression, Arumberia (Bland 1984; McIlroy & Walter 1997; McIlroy et 286

al. 2005; Kolesnikov et al. 2012), and in refining the geochronological record of the locality, 287

are ongoing areas of research for his group. He passed away before embarking on the next 288

phase of our Longmyndian investigations—an opportunity to compare the sections to thick 289

non-marine Ediacaran successions in Newfoundland—but he would have been amused to 290

note that, as in all known non-marine Ediacaran successions, there is currently no evidence 291

for the classic Ediacaran macrobiota. Had the Ediacaran biota truly been composed of lichens 292

(Retallack 1994), environments like this are surely amongst the most likely places where we 293

would have expected to find them. 294

295

Newfoundland, Canada 296

In addition to the work on rangeomorphs mentioned previously, Martin supported the 297

exploration of sites in Newfoundland by his students. Research into Ediacaran taphonomy, 298

largely using data collected from Newfoundland, offered a comprehensive assessment of how 299

taphonomic processes and styles changed across the Ediacaran–Cambrian boundary, and their 300

impact on our interpretation of the fossil record (Callow & Brasier 2009a). Martin also 301

contributed to the recognition that some impressions on Ediacaran fossil-bearing surfaces 302

previously described as valid taxa (e.g. Ivesheadia, Shepshedia and Blackbrookia; Boynton & 303

Ford 1995) instead reflect decayed carcasses of other Ediacaran organisms (Liu et al. 2011; 304

though see Laflamme et al. 2011; Wilby, et al. 2011). The recognition that time averaging 305

occurs on Ediacaran bedding planes was a revolutionary idea at the time, and has been built 306

upon by several other studies recognising the presence of multiple successive communities 307

preserved on individual Ediacaran bedding planes (e.g. Antcliffe et al. 2015; Wilby et al. 308

2015). It has also inspired studies into the potential ecological impact of the appearance (and 309

post-mortem influence) of macroscopic soft-bodied organisms on both benthic communities 310

and the late Ediacaran carbon cycle (e.g. Liu et al. 2015a; Budd & Jensen 2015; Dufour & 311

McIlroy this volume). 312

Martin and his students have also made significant contributions to the Ediacaran 313

ichnofossil record. The description and interpretation of 565 Ma horizontal surface trails in 314

the Mistaken Point Formation of Newfoundland (Liu et al. 2010a; Liu et al. 2014a), and of 315

~560 Ma vertical equilibration traces in the Fermeuse Formation (Menon et al. 2013), extend 316

the record of metazoan movement considerably into the Ediacaran Period. Those discoveries 317

provided a search image for Ediacaran researchers that appears to have stimulated a 318

considerable increase in the recognition of late Ediacaran trace fossils worldwide (e.g. Chen 319

et al. 2013; Carbone & Narbonne 2014; Macdonald et al. 2014; see Liu & McIlroy 2015), 320

providing some of the strongest existing evidence for the presence of motile metazoans 321

among the largely sessile Ediacaran macro-organisms. However, Martin was wary of 322

accepting all claims for complex metazoan movement or feeding, staying true to his belief 323

that the null hypothesis must first be rejected before considering more ground-breaking 324

claims (Brasier 2015). He was involved in questioning both ‘grazing’ traces of Dickinsonia-325

like organisms (McIlroy et al. 2009), and claims for bioturbation in Siberian rocks (Brasier et 326

al. 2013a). These challenges were nevertheless constructive, and were intended to spur 327

debate that will ultimately resolve the nature of these important materials. 328

Martin oversaw the description of discoveries of communities of juvenile 329

rangeomorphs within the Mistaken Point Ecological Reserve (Liu et al. 2012), and personally 330

discovered the holotype of what would come to be known as Haootia quadriformis (Liu et al. 331

2014b) on the Bonavista Peninsula. This remarkable fossil caused a lot of head-scratching 332

and beard-stroking, but upon discovery of a second specimen in 2013, an interpretation of 333

Haootia as recording an organism with fibrous musculature was developed (Liu et al. 2014b, 334

2015b). Once again, Martin was keen to ensure that the null hypothesis was first rejected 335

before he would seriously consider options that implied the presence of metazoan 336

musculature, and even after publication he was careful to stress that this interpretation was a 337

“tentative reconstruction”, made on the basis of available evidence. His demand for high 338

standards continued throughout his Ediacaran research, for example in his questioning of the 339

terrestrial interpretation of the Ediacaran biota (e.g. Retallack 2010, 2013). He considered 340

such interpretations to require special pleading to reinterpret sections that, on process-based 341

physical sedimentological evidence, have always been considered marine (e.g. Liu et al. 342

2010b; Callow et al. 2013). 343

Palaeoenvironmental and preservational context was central to Martin’s approach to 344

fieldwork, and he would encourage his students to visualize fossil assemblages in their 345

original depositional environments, expertly producing impromptu sketches of possible 346

scenarios in his notebook after meticulously recording his field observations (e.g. Fig. 4). 347

This broad consideration of palaeoenvironment and context formed an important counterpoint 348

to the detailed study of individual Ediacaran fossils. His work on both was driven by a 349

combination of detailed observation, imagination, and biological insight, guided and 350

tempered by his wide experience. An example of his rapid assimilation and interpretation of 351

new observations is given by the reinterpretation of the remarkable preservation of Ediacaran 352

rangeomorphs at Spaniard’s Bay (Brasier et al. 2013b). An observation by one of his students 353

that the basal discs of fronds preserved on this surface show a steep undercutting on one side 354

struck him immediately as of significance, and led to his proposing a hydraulic model, which 355

the group tested and confirmed with sedimentological and morphological evidence. This 356

reassessment of the context of preservation has important implications for the interpretation 357

of morphological features in Ediacaran rangeomorphs (e.g. compare discussions in Brasier et 358

al. 2013b with those in Narbonne et al. 2009). In addition to studying the fossils and their 359

sedimentological context, Martin, along with Duncan McIlroy and Jonathan Antcliffe, had in 360

recent years developed hypotheses regarding the role of geochemical cycling in Ediacaran 361

ecosystems (Dufour & McIlroy this volume). These hypotheses are currently being tested 362

through the application of NanoSIMS to investigate sulfur cycling, in collaboration with 363

David Wacey, using material from Newfoundland in particular. This line of research was in 364

its infancy at the time of Martin’s death, but had begun to yield preliminary results by 365

demonstrating the biogenic origin (via microbial sulfate reduction) of pyrite framboids within 366

mineralized veneers at macrofossil-bearing interfaces (Wacey et al. 2015; see also Liu 2016). 367

Further sulfur isotope data will be published in the coming years as this avenue of research is 368

explored in greater detail. 369

Martin’s work in Newfoundland led to his being invited along with Alex Liu to write 370

the Global Comparative Analysis of Ediacaran Fossil Sites for the Government of 371

Newfoundland and Labrador: a document that in 2015 was submitted to UNESCO as part of 372

the Canadian nomination of Mistaken Point Ecological Reserve for World Heritage Site 373

status (Liu & Brasier 2012). As well as comparing Ediacaran fossil sites worldwide against a 374

number of palaeontological criteria, the report set out a protocol for the assessment of the 375

Outstanding Universal Value of Precambrian fossil sites, which Martin hoped would make a 376

lasting contribution to society’s appreciation of important palaeontological localities 377

worldwide. 378

379

Considering the interplay between Earth and Life 380

Core to Martin’s thinking when assessing Ediacaran and Cambrian evolutionary events was 381

the interplay between evolution and the wider biosphere. He realized that the patterns 382

revealed in the fossil record could only be deciphered through consideration of the 383

contemporaneous geological and geochemical events that triggered, or were consequences of, 384

evolutionary innovations. His deep musing on approaches to interpreting the fossil record, 385

which he regarded as akin to playing a card game without knowing the rules (see Antcliffe et 386

al. this volume), was reflected in his public lectures and nicely summarised in his popular 387

science book on the subject, Darwin’s Lost World (Brasier 2009). In this book, intended to 388

inspire new generations of students as well as the general reader, he highlighted the dramatic 389

impact of the evolutionary innovation of predation among early animals, driving an arms race 390

of attack and defence mechanisms and culminating in the “circus of worms”—the sudden 391

appearance of widespread and deep burrowing—that so strikingly characterizes the transition 392

from the Ediacaran to Cambrian (Herringshaw et al. this volume; McIlroy & Brasier this 393

volume). His perspective was profoundly influenced by an Earth Systems view, involving 394

feedbacks, symbiotic associations, and the possibilities of catastrophic collapses of 395

interconnected webs resulting from subtle internal as well as external factors. These ideas, 396

many of which stem from observations made during his time as a ship’s naturalist, fed even 397

more strongly into his second book, about the origins of complex life, Secret Chambers 398

(Brasier 2012). 399

400

The forcing factors for animal evolution and the Cambrian Explosion 401

A particularly long-running strand of Martin’s research was his investigation of whether the 402

Cambrian Explosion was a real event, and what may have triggered it. Over two decades, 403

Martin continually refined his ideas towards a sophisticated synthesis of intricately 404

interconnected phenomena, which together provided the environmental context for the 405

evolutionary diversification of animals. Some of his earliest work investigated the role of sea 406

level change and facies variations in driving the Cambrian Explosion (Brasier 1982). 407

Extensive erosion continues to be explored as a tenable trigger for the Cambrian radiation 408

(e.g. Peters & Gaines 2012). Martin later considered the impact of factors such as climate 409

change, carbon cycle instability, eutrophication and anoxia (Brasier 1991, 1992), and even 410

supercontinent amalgamation (Brasier & Lindsay 2001), the latter in part informed by his 411

previous work collating the distribution of fossils and facies in several regions to assist in the 412

assembly of widely cited Neoproterozoic to Palaeozoic palaeogeographic reconstructions 413

(McKerrow et al. 1992; Torsvik et al. 1996). The occurrence of a broad belt of glauconite 414

and phosphate-rich sedimentary facies in the Early Cambrian was a long-lasting source of 415

inspiration and intrigue (Brasier 1980, 1992; Brasier & Callow, 2007), and Martin’s favourite 416

question for speakers on Ediacaran–Cambrian topics at conferences was “but what about the 417

phosphate?”, a question he argued could be asked with justification of any researcher of this 418

interval. Martin’s observations of the apparent onset of phosphatization at shallow depths 419

within the sediment profile led him to invoke nutrients such as phosphate as a potential 420

trigger for the Cambrian Explosion and the advent of biomineralization (Brasier 1980, 1990, 421

1992). Whether phosphate deposition was a cause (Brasier 1992) or a consequence (e.g. 422

Butterfield 2003) of the Cambrian radiation has yet to be resolved, but Martin undoubtedly 423

caused many to ponder the fundamental importance of nutrients for evolution (e.g. Tucker, 424

1992; Boyle et al. 2014). Resolving the role of phosphate in fossilization (Brasier 1984, 1985, 425

1990) and oxygenation (Brasier & Callow 2007) became another long-running theme of 426

Martin’s research, and was used as a primary example of his hypothesis that the nature of the 427

fossil record has changed through time (cf. Callow & Brasier 2009a; Brasier et al. 2011). He 428

recognised that soft-bodied forms are preserved by phosphate in exquisite detail from the 429

Early Cambrian to the late Mesoproterozoic, and suggested that the quality of the fossil 430

record (somewhat paradoxically) improves the further back in time we go (Brasier 2009). 431

432

Going forward 433

At the time of his death, Martin’s research into the Ediacaran–Cambrian transition was far 434

from over, and there remains much to do to understand evolutionary events and processes 435

during this interval. We have touched upon several of the ways in which studies Martin was 436

involved in are already being built upon (e.g. Dufour & McIlroy this volume). However, 437

Martin’s greatest legacies in this field are arguably his involvement in defining the 438

Ediacaran–Cambrian boundary (and also the basal Ediacaran GSSP in his role as a voting 439

member of the Ediacaran Subcommission), and his support and expansion of the Ediacaran 440

scientific community, both through the guidance of members of his own group, and the 441

encouragement he offered, both informally and in reviews, to many scientists around the 442

world seeking to tackle Ediacaran–Cambrian problems. 443

Martin’s work questioned several of the hypotheses that were ‘in vogue’ at the time, 444

for example the severity of Neoproterozoic Snowball Earth events (Leather et al. 2002; Allen 445

et al. 2004; Kilner et al. 2005). Importantly, in the best scientific tradition, he was not above 446

questioning his own previous interpretations, for example revoking specimens he had earlier 447

described as peristaltic burrowing (Brasier & McIlroy 1998; then see Brasier & Shields 2000) 448

and the oldest sponge spicules (Brasier et al. 1997; then see Antcliffe et al. 2014). In much 449

the same way as his approach to palaeobiology in general, Martin’s Ediacaran–Cambrian 450

work challenged existing paradigms, expanded knowledge via application of new techniques 451

to known sections, and provided novel hypotheses for critical testing. His studies throughout 452

his career were rigorous, vigorous, thought-provoking, and scholarly. They often combined 453

strong fieldwork elements in order to provide essential context for palaeontological material 454

with the development of theoretical frameworks through which to make sense of the unusual 455

organisms and events. This approach is something that many of his former students are keen 456

to uphold. At its core, Martin’s Ediacaran–Cambrian work was focused on pushing the 457

boundaries of knowledge: “trying to guess what lies over the hill and map terra incognita”, 458

and ultimately understand the questions of how and why animals evolved. He may not have 459

answered those questions completely, but he certainly played a prominent role in steering the 460

scientific community towards the solutions. 461

462

Acknowledgments 463

We thank Palaeocast for making public their recordings of Martin’s Lyell Lecture at his 464

retirement event at the University of Oxford in September 2014, from which several of the 465

quotes in this article were taken, and the Geological Society of London, whose website 466

records Martin’s formal Reply upon receiving the Lyell Medal in 2014. Simon Harris of the 467

British Geological Survey provided an image for Figure 3a, and Per Ahlberg kindly provided 468

information on Martin’s Cambrian Subcommission activities. 469

470

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824

Figure captions 825

826

Fig. 1 Martin Brasier in Newfoundland. (a) On the ‘E’ Surface at Mistaken Point, in his 827

socks, 2005. (b) Sketching on the Bonavista Peninsula, 2008. Photo credit: Jack Matthews. 828

829

Fig. 2 (a) Martin (inset) undertaking laser scanning in the field, Memorial Crags, Charnwood 830

Forest, Leicestershire. (b) An example of a laser-generated digital image: the holotype of 831

Charnia masoni (see Brasier & Antcliffe 2009). 832

833

Fig. 3 Martin’s method of drawing Ediacaran fossils, as exemplified by his work on the 834

holotype of Charniodiscus concentricus, from Charnwood Forest, Leicestershire. (a) 835

Photograph of a cast of the holotype specimen in New Walk Museum, Leicester, image 836

courtesy of the British Geological Survey. (b) Martin’s sketch of the key features of the 837

specimen, developed via drawings made from photographs and laser scan data. (c) Martin’s 838

novel interpretation of multiple fronds emanating from the stem of the organism. 839

840

Fig. 4 Excerpt from one of Martin’s (many) field notebooks, showing a log drawn through 841

the fossil-bearing section at Spaniard’s Bay, Newfoundland (work that was eventually 842

published in Brasier et al. 2013b). 843